Contribution of Na+ counterions to H-AOT&Na-AOT-based W/O microemulsion formation using aqueous NaOH solutions as estimated by pyranine absorbance

Jun Oshitani, Shiho Takashina, Mikio Yoshida, Kuniaki Gotoh

研究成果査読

抄録

The objective of this study is to estimate the contribution of Na+ as a counterion in the formation of H-AOT&Na-AOT-based W/O microemulsions using aqueous NaOH solution by pyranine absorbance measurements. A mixture of an aqueous NaOH solution containing pyranine/H-AOT&Na-AOT/isooctane was emulsified by changing the mixing ratio of Na-AOT (XNa-AOT = 0-1) and the mole fraction of NaOH (XNaOH = [NaOH]/the AOT- concentration in the water pool = 0-1). The phase behavior of the emulsified mixture was evaluated from the absorbance of pyranine at the isosbestic point and by visual observations. W/O microelumsions are formed at the mid-range of XNa-AOT, whereas the emulsified mixture separates into two phases at lower XNa-AOT and higher XNa-AOT. The two phase boundaries shift toward lower XNa-AOT as with increasing XNaOH. The phase behavior depends on the degree of screening of electrostatic repulsions between the polar headgroups of AOT- by the Na+ counterion. Interestingly, nano-sized W/O microemulsions are formed without phase separation using a highly concentrated NaOH aqueous solution when the Na-AOT mixing ratio is appropriately adjusted. The phase behavior was plotted as XNaOH versus XNa-AOT, and the correlation equations for the two phase boundaries were obtained by fitting the points. The contribution of the Na+ counterion from NaOH to W/O microemulsion formation was estimated by the correlation equations. The absorbance of pyranine and the size of W/O microemulsions, as measured by DLS, were plotted as a function of XN a+ = (x [ N a+ from NaOH ] + [ N a+ from Na-AOT ]) / [ AO T- ], in which x is the ratio contributed by NaOH. The absorbance and size correlates well with XN a+, indicating that XN a+ is a meaningful parameter for quantitatively estimating phase behavior and size variation.

本文言語English
ページ(範囲)136-140
ページ数5
ジャーナルColloids and Surfaces A: Physicochemical and Engineering Aspects
350
1-3
DOI
出版ステータスPublished - 10月 20 2009

ASJC Scopus subject areas

  • 表面および界面
  • 物理化学および理論化学
  • コロイド化学および表面化学

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